Abstract

The observation of subharmonic emissions during an ultrasound experiment has often been taken as the sine qua non of stable cavitation. While the appearance of subharmonics is very likely the indication of the presence of bubbles, it leads to a thorny question: What do subharmonic emissions tell us about the nature of the cavitation in the experiment? The answer to that question will naturally be of pragmatic importance to the experimenter seeking to enhance, inhibit, or otherwise control the resulting bioeffect. In this talk, we review the physical mechanisms for bubble generation of subharmonics, giving where possible, examples of each mechanism and eliciting the consequences for biomedical experiments.